The present invention relates generally to the control of friction elements in order to accomplish ratio changes in an automatic planetary transmission. More particularly, the present invention relates to the direct computer control of multi-speed transmission friction elements through the use of hydraulic devices to accomplish ratio changes in an automatic planetary transmission.
Automatic transmissions for motor vehicles are arranged to shift gears automatically, dependent on running conditions of the motor vehicle, to achieve desired vehicle running characteristics. It is customary to provide a ratio changing event map composed of upshifting and downshifting strategies for each gear position. The strategies are established in relation to the vehicle speed/operator commands engine/power output, so as to control the automatic transmission to change ratios according to the ratio changing event control strategies.
One type of automatic transmission includes a power transmission system comprising a plurality of power transmission paths (e.g., a plurality of gear trains), a plurality of ratio changing devices (e.g., a plurality of hydraulically operated clutches) for selecting the power transmission paths, and a control mechanism (e.g., a hydraulic pressure control valve) for controlling the operation of the ratio changing devices. When operating conditions of a motor vehicle are transitory within a predetermined ratio changing event strategy, ratio changing commands are produced to effect an upshift or a downshift, and a solenoid valve is operated based on the ratio change command to control operation of the hydraulic pressure control valve to engage one of the hydraulically operated clutches. The power transmission path through a certain gear train associated with the engaged clutch is then selected to effect a ratio change.
The gear ratio of the previous gear position (which is established by a power transmission path or gear train that has been selected until a ratio change command is issued), and the gear ratio of a next ratio position (which is established by a power transmission path or gear train selected by the ratio change command) are different from each other. Therefore, it is important that the transmission ratio changing event be carefully controlled in order to avoid event shock or delay when a ratio change is made from the previous position to the subsequent position. The timing of the shift, which is controlled by one friction element coming off and another friction element coming on is therefore critical to efficient operation of an automatic transmission.
Efforts to control the operation of the control mechanism (e.g., the pressure control valve) in an attempt to provide efficient timing and, therefore, to eliminate any ratio change event shock or delay, have employed a variety of mechanisms. One such known mechanism involves the use of a variable force solenoid. A typical variable force solenoid receives a control signal from an ECU which in turn controls the pressure control valve to communicate with and control the pressure profile to selected friction elements, in order to engage the proper gear. However, this method relies on the receipt of information from the pressure control valve as to the vehicle operating conditions, in the form of feedback. Based on this feedback, a pressure control signal is transferred in order to control the output of the solenoid valve to generate the required pressure profile. This type of control system is relatively complex. The prior mechanisms and systems also suffer from the inability to provide consistent functional characteristics.
Another known mechanism for controlling a pressure control valve is a simple on/off solenoid which signals a hydraulic control system to control the operation of a friction element to engage or disengage as dictated by a specific pressure profile activating the appropriate gear. This type of control system is also relatively complicated and complex. These prior mechanisms and systems also suffer from the inability to provide consistent functional characteristics.
Additionally, typical pumps that are used in current automatic transmissions are driven directly by the engine. The typical transmission pumps are thus always running at engine speed, resulting in parasitic losses for a majority of a typical duty cycle. This is because current pumps are sized for worst case mode of operational envelope, which is typically only a small portion of the time. It would thus be advantageous to provide an automatic transmission that provides precise control of the ratio changing events with a system that is compact, efficient, consistent, and relatively simple.
It is, therefore, an object of the present invention to provide a highly responsive electro-hydraulic pump for multi-speed transmission friction element control that is computer controlled.
It is another object of the present invention to provide a modular electro-hydraulic pump for multi-speed transmission friction element control that provides improved efficiency and decreased parasitic loss.
It is yet a further object of the present invention to provide an independent system that mitigates against undesirable fluctuation in operation fluid temperature.
It is still a further object of the present invention to provide a modular electro-hydraulic pump for multi-speed transmission friction element control that requires a smaller space envelop than prior systems and also provides effective thermal management.
It is yet another object of the present invention to provide for multi-speed transmission friction element control that operates in real time to provide on demand pressure profiling as desired.
In accordance with the above and other objects of the present invention, an electro-hydraulic pump element for use with an automatic power transmission is provided. The pump element includes a fluid source having a quantity of fluid stored therein. The pump element includes a plurality of individual pump elements each having a respective inlet end and a respective outlet end. The fluid source is in communication with each of the inlet ends of the plurality of pump elements via a passageway in order to convey fluid thereto. The outlet ends of each of the plurality of pump elements is in communication with a respective switching valve in order to distribute the fluid flow and specific pressure profile to a respective friction element, as required to accomplish ratio changing. The plurality of pump elements and the switching valves are each in communication with an electronic control module for control thereof, whereby the electronic control module activates an appropriate one of the plurality of pump elements and an associated switching valve to direct fluid to the necessary friction element as determined by the control module.
These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and appended claims.